Nice of you're the author and you want to keep some control over your work. You can be pretty sure that your document will always look like it did when you put it out into the ether. No pictures popping down to the next page and no additional commentary slipped into the text unnoticed.
But what if you're the reader, or user of the document. Maybe you want to lift something out of it and use it in your own document. (That's not necessarily evil -- it could be data from a government report, or something else that's in the public domain). Or you might want to cut out some paragraphs so printing it doesn't use up so much paper. You might even want to combine a few PDFs so you have all of the information in one place.
Or forget about all that stuff, what if you just want to read a PDF quickly. Adobe Reader is more than 20 megabytes just to download. (Plus, Adobe tries to slip in its Album Starter Edition for another 7 megabytes).
That's a big program. It takes up a lot of space on your hard drive, then it takes time to load -- and that's even if you leave a little bit of it in memory for "quick starting" it.
Sumatra PDF (Free, Open Source)
Sumatra is slick. It's simple, small, super-fast and open source. It takes up just 895 KB on your hard drive.
What can it do? I'll print the entire manual:
- open PDF files via menu
- open PDF files via drag & drop
- page up and 'p' for going to previous page
- page down and 'n' for going to next page
- 'q' to quit
- set different zoom levels via menu
I made it my default PDF reader (it asks the first time you fire it up). That way I can check out a PDF document quickly. Most of the time that's all I need to do. If I need to do more, I have a program for that too.
This is a step up from Sumatra. It's a little bigger (2MB), and it does a little more. You can cut and copy from PDF documents, move words around, move images and add things. Here's the catch: you can make all of those changes, but you can't save the result. You can print it, though and that's handy.
If you want to save your work, you have to upgrade to PDF-Editor. It's $80 bucks and probably worth it. I don't use it. If there's something specific you want to do with pdfs and you don't want to fork over the full $80, the company has a whole line of PDF software that does various things for less money. It's all affordable and you can try it before you buy it. (Incidentally, the company, CAD-KAS Software, has a whole line of interesting-looking programs, mostly in the $10 - $20 range).
So why don't I upgrade to PDF-Editor? Two reasons. First, PDF-Editor had a few hiccups right after I installed it. It seems to be OK now, but I want to use it for a while before I consider upgrading.
ABBYY PDF Transformer ($100)
The other reason is that I already own ABBYY PDF Transformer. The main thing I need to do with PDFs is convert them to text. Formatted text -- because I'm usually working with tables of data that I want to put into a spreadsheet. PDF Transformer does that really well.
Creating PDF Files
By the way, if you just want to create PDF files, that's easy and free. Some software (like Microsoft Office and Open Office) hve plug ins that let you print to PDF. You can also get little programs that show up like printers in all of your software and let you "print" your work into PDF. Instead of coming out of your printer on paper, they turn into a PDF document on your computer.
Cute PDF (Free)
You just install this freeware and the open-source Ghostscript converter and any program that prints will print to PDF. It's nice because it doesn't harass you about upgrading or hit you with advertising. It just does what it's supposed to do. You can upgrade though.
Adobe Reader (Free)
This is the PDF reader nearly everybody uses. It works, it lets you do a few things with PDF documents (read them, print them, copy text (awkwardly and without the formatting), and copy images). But it's big and slow.
Adobe Acrobat ($300 and up)
This is the program that probably created the PDFs you read. It lets you create, combine, edit, and annotate PDFs. You can also convert a PDF to a text document (e.g. Word) with the formatting intact.